Although they work in similar ways, each oral medication has a slightly different chemical makeup. These minor differences affect the way each medication works, such as how quickly it takes effect and wears off, and the potential side effects. Your doctor will consider these factors as well as other conditions you have and possible interactions with other medications you take. Sildenafil: This medication is most effective when taken on an empty stomach one hour before sex. fildena 100 onlineand cenforce 150mgeffective for four to five hours or more if you have mild to moderate erectile dysfunction.Vardenafil: This medication also is most effective when taken one hour before sex and can be taken with or without food. A high-fat meal might keep it from absorbing as quickly. Vardenafil is effective for four to five hours or more if you have mild to moderate erectile dysfunction. A newer form of the drug that dissolves on the tongue might work faster than the pill that you swallow. Tadalafil: This medication is taken with or without food about one to two hours before sex. It's effective for up to 36 hours. It can be taken in a small dose daily or in a larger dose as needed. Avanafil: This medication is taken with or without food 30 minutes before sex, depending on the dose. It lasts up to six hours. Because these drugs are similarly effective, the American College of Physicians recommends that the choice be based on your preferences, including cost, ease of use, how long the drug's effects last and side effects. There are generic versions of sildenafil, vardenafil and tadalafil available ononcohiv.